[71 T/A]

I'm talking a classic Pontiac that gets driven 1,000-1,500 miles a year like my stock 69 GTO with T400.

[02Hawk]

every 100 years....joke....5 years

[geeteeohguy]

I would do a trans service (pan and filter with 4 quarts of new fluid) every 15-20,000 miles, regardless of time.

[My442]

Get a MityVac fluid evacuator, and suck the pan dry and refill once a year. No getting dirty.

Change the filter every 3 years.

[455Grandville]

If it's clean & red leave it be .

[Tim Corcoran]

If it's clean & red leave it be . X2

[Cliff R]

+3

Never change it. If/when the trans starts slipping enought to blacken up the fluid....rebuild the transmission....Cliff

[Fishin2Deep4U]

I have always changed my street cars at around 20K and no more than 3 years. Track cars much more often. I like to use trans heat as a guide for changes. Lots of time sitting on the convertor in traffic? Gonna need more changes.

I do not buy into the theory that clean and non-stinky fluid is okay. JMO.

I have seen more than once just changing fluid intervals a few thousand miles can greatly increase the life of the trans. Even in a more severe use trans like the one in my 700+HP Dodge diesel responds to more immediate fluid changes. And I have a lockup convertor which greatly lowers cruising temps. Of course I have built more than a few performance units for the high performance diesel crowd.

I do also realize most "classic" car guys don't put enough miles on to really worry about it either way.

Dave

[Half-Inch Stud]

Originally Posted by Cliff R

+3

Never change it. If/when the trans starts slipping enought to blacken up the fluid....rebuild the transmission....Cliff

Drop the pan to change the FILTER if the transmission is acting up.

IF the fluid has turned away from Red (brown for 150k+ miles) then you COULD change the fluid, and you will feel better (trans will feel the same).

IF the fluid has "LOTS OF metal" pieces with the particulate, then the Converter is likely bad, so "change the fluid" while replacing the converter.

[Cliff R]

Unlike engine oil, transmission oil is NOT contanimanted with blow-by products of combustion like engine oil, carbon, water, etc.

It's a hydraulic system, with full filtered fluid to the internals. It doesn't need to be changed in most cases, at least when it comes to muscle cars.

If you are running a really loose converter, and "cooking" the fluid in your old GTO, get a better converter for the GTO's transmission.

Some folks get a "warm and fuzzy" changing the fluid in their old TH400's and TH350's. You are really only changing the filter, and at most about 1/3rd of the fluid, because most of the fluid is trapped in the converter and under the valve body/trans internals.

I'm not saying here it's a bad idea, but really not needed in most cases with these sort of vehicles......Cliff

[My442]

I use the Mityvac "suck the pan dry" process for all my cars.

My 1999 F150 has 170,000 miles, and the tranny shifts like new.

The issue is that transmission fluid does get dirty from wear items in the unit, as well as moisture. If you open up a torque converter from a high mileage car that has not had tranny service, you will find that sludge builds up inside the vanes.

4 quarts of fluid is about $15, once a year...a lot cheaper than a tranny rebuild.

[GT182]

And the filter will clog up with sludge too. Best to change the filter and fluid like the manufacturer recommends.... or sooner.

[Schurkey]

I change fluid at something like 100,000 miles. Fresh filter at the same time.

Re-fill the trans with 5 quarts, have more quarts open 'n' ready to pour.

Drop the trans cooler tube on the OUTPUT side of the cooler, install temporary tube from cooler to drain pan.

Start engine, dump more fluid into the trans. Watch fluid coming out of temporary tube. When it looks clean, I kill the engine and re-connect the cooler tube. Top off fluid as required.

Trans, including converter and cooler is now flushed and has new filter.

15,000 miles/ 5 years is crazy.

[Half-Inch Stud]

Originally Posted by My442

...If you open up a torque converter from a high mileage car that has not had tranny service, you will find that sludge builds up inside the vanes...

I cut-open a pair of 1970 TH400 Converters and both were SPOTLESS on sludge & wear. Well inspection; like testing hand grenades huh.